linux-kernel - Re: [PATCH V3] mm: Allow userland to request that the kernel clear memory on release

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Message-ID: <CACdnJuuVBb8bOUGGq0H+Ask_ufT3X9YH42o5nAGQK0TCf+aKWg@mail.gmail.com>
Date:   Fri, 26 Apr 2019 11:10:22 -0700
From:   Matthew Garrett <mjg59@...gle.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     linux-mm@...ck.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH V3] mm: Allow userland to request that the kernel clear
 memory on release

On Fri, Apr 26, 2019 at 12:45 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> On 4/26/19 12:58 AM, Matthew Garrett wrote:
> > Updated based on feedback from Jann - for now let's just prevent setting
> > the flag on anything that has already mapped some pages, which avoids
> > child processes being able to interfere with the parent. In addition,
>
> That makes the API quite tricky and different from existing madvise()
> modes that don't care. One would for example have to call
> madvise(MADV_WIPEONRELEASE) before mlock(), otherwise mlock() would
> fault the pages in (unless MLOCK_ONFAULT). As such it really looks like
> a mmap() flag, but that's less flexible.
>
> How bout just doing the CoW on any such pre-existing pages as part of
> the madvise(MADV_WIPEONRELEASE) call?

I'll look into the easiest way to do that.